I doubt you will ever find a politician more desperate to believe Nietzsche's aphorism that whatever doesn't kill us makes us stronger than Mitt Romney.

With former Pennsylvania senator Rick Santorum announcing that he is suspending his presidential campaign, it ensures what many political observers have assumed for quite some time – that Mitt Romney will be the Republican nominee for president this autumn. Only 26 other men have achieved this goal, so congratulations to Romney are in order. But a larger view of Romney's political situation takes some of the bloom off this particular rose. Have the past 12 months of campaigning – while certainly not killing him – really made Romney stronger? So far the evidence is not very good.

Only 34% of Americans have a positive view of Romney, which makes him at this point in the presidential campaign one of the least popular presumptive nominees in American history. Even candidates who lost (and lost badly) such as Dukakis in 1988, Dole in 1996 and McCain in 2008 were more popular than Romney is right now. More disconcerting still is the fact that even Republican rank-and-file voters are somewhat indifferent to Romney. His favourability among Republicans overall is a rather tepid 62%. Those who define themselves as conservatives within these ranks have an even less favourable view, with 47% viewing their party's nominee in a positive light. On the other side, Obama has none of the same problems with a sparkling 86% favourability among Democrats.

Granted, most of these traditional Republican voters will cast a ballot for Romney in November, but it also means that he must spend some of his precious time over the next few months rallying conservatives behind him, to ensure they turn out in droves. On a practical level, this results in Romney not only needing to dent the relatively high favourability ratings of his opponent, but also having to rehabilitate his own.

And he will be doing this against a candidate who is a far cry from the collection of also-rans, fringe politicos and pizza magnates he squared off against in the Republican primary. Barack Obama is not Rick Santorum and in the days since the latter departed the race, the president's campaign has put out a host of tough videos attacking Romney for his dalliances with the truth, the extolling of his conservative bona fides and even his lack of support for female pay equality. With Obama planning to raise hundreds of millions of dollars (some say it might go as high as a billion), it's a good preview of the escalating attacks on Romney that are certain to come over the next seven months. Romney's days of outspending his opponents and carpet-bombing them with negative ads have ended.

All of this suggests that the road ahead for Romney will be extremely difficult (though not insuperable). Still, as bad as Romney's poll numbers are – and as formidable as his opponent is – that doesn't actually tell the whole story of his political weakness. From a policy perspective, the slowly improving economy has undercut his key campaign message, namely his intent to run against the economic downturn. In recent weeks, Romney has been reduced to saying that the latest economic improvement would have been stronger if he were in the White House; a legitimate argument but one that is a bit too nuanced for the presidential campaign trail.

But the even greater problem is one that Romney inflicted upon himself. This started in December when Newt Gingrich was rising in the political polls and threatening Romney's stranglehold over the nomination. One of the charges the Romney camp used against the former Speaker was that he wasn't sufficiently conservative. It was an odd charge given that Romney had signed a comprehensive healthcare bill remarkably similar to Obamacare and, as a candidate in Massachusetts, had indicated support for abortion rights as well as gun-control measures.

None the less, the Romney team saw Gingrich as vulnerable because he had come out against the House Republican budget passed last spring, which would end the federal guarantee for Medicare recipients (beginning with those under the age of 55) and eviscerate much of the social safety net and modern welfare state in America. The budget, which is generally referred to as the Ryan budget, named after House Republican budget chairman, Paul Ryan, was and remains a toxic political document and one whose key measures are opposed not only by Democrats and independents but also by a wide swath of Republicans. Still, the opportunity to outflank Gingrich on the right – a move similar to what Romney had done on immigration against Texas governor Rick Perry – was too juicy to pass up. And since then Romney has only increased his support for the Ryan budget – going so far as to call it "marvellous".

There's a good possibility that this could be the most damaging act by Romney in his quest for the presidency. Indeed, it wasn't Romney's various and embarrassing gaffes that were the centrepiece of President Obama's speech to the Associated Press – which represented the nominal kick-off to the autumn campaign – it was the Ryan budget and his none-too-subtle effort to link it to Romney.

Calling the budget a Trojan horse, disguised as a deficit-reduction plan, Obama said that the legislation is "really an attempt to impose a radical vision on our country. It is thinly veiled social Darwinism. It is antithetical to our entire history as a land of opportunity and upward mobility for everybody who's willing to work for it; a place where prosperity doesn't trickle down from the top, but grows outward from the heart of the middle class. And by gutting the very things we need to grow an economy that's built to last – education and training, research and development, our infrastructure – it is a prescription for decline."

Obama's speech also covered all the areas of government that would be reduced by the Ryan budget – Head Start (a comprehensive programme for low-income families), support for education, measures to fight crime, laws that protect food and safety, Medicare and Medicaid, and even national parks. As Obama noted: "If this budget became law, by the middle of the century, funding for the kinds of things I just mentioned would have to be cut by about 95%… as a practical matter, the federal budget would basically amount to whatever is left in entitlements, defence spending and interest on the national debt – period."

This is a potent political argument because even though both parties like to disparage "big government" and voters regularly decry the overweening influence of the federal government on the lives of the American people, in reality Americans love government spending and they love federal programmes. They love Medicare; they love Medicaid; they love social security; they love education, transportation and environmental regulations. With the sole exception of foreign aid (and this is largely because they overestimate how much of the federal budget goes to it), the American people are actually quite besotted with big government.

This is a regular trap into which conservative Republicans fall, namely believing that when voters nod their heads at calls for cuts in government spending they actually want politicians to do just that when they get into power. And one might expect such behaviour from blinkered ideologues such as Paul Ryan and his Tea Party cohorts in the House of Representatives.

But Mitt Romney, to put it bluntly, should know better. That he has embraced a piece of legislation likely to cause him so much damage in November is a telling indication of his larger – or, rather, lesser – political skills. But in his defence, it's also an indication of how conservative the Republican party has become. According to a recent survey by Keith Poole and Howard Rosenthal, political scientists from respectively the University of Georgia and New York University, the Republican party is more conservative than at any point in the last century.

None of this necessarily means that Romney is finished. There are already some indications that the economic recovery might be faltering and a major event from "outside" the campaign (such as the Supreme Court overturning Obamacare) could hamstring the president. Moreover, Obama's approval ratings are barely at 50%, which is hardly laurel-resting territory.

Still, the Republican contender begins his pursuit of the White House on remarkably shaky political ground – buffeted by the statements and promises that he made to capture the nomination of a party that is radically conservative. That, more than anything else, may be what kills his presidential dreams in the end.

Michael Cohen is author of Live From the Campaign Trail: The Greatest Presidential Speeches of the 20th Century.